Cavityless molding performed with consumable patterns has several distinct advantages, the chief of which is that the shape to be cast may take any configuration. Molding, itself, comprises ramming the sand or other suitable molding material around the pattern without regard to a parting line or pattern draft. This allows for considerable decrease in the cost of molding, particularly for parts where a single casting is required from a given pattern. Typically, the expendable pattern is made from an expanded plastic material such as expanded polystyrene beads or polyethylene, which is, as is well known, porous because it contains air voids in the expanded condition. The material is light weight, economical and easy to form into any desired bulk configuration. The pattern material is capable of being volatilized or burned, particularly in the absence of oxygen without appreciable residue remaining. Accordingly, when the molten metal is poured into the molding box, the pattern is consumed more gradually by the advancing molten metal so that the mold box is never with a void therein and therefore is identified as the cavityless molding method.
This mode of casting has achieved great economic advances when performed with patterns which are unitary or have extremely large openings which can be freely filled with sand during the flask filling operation. That is to say, commercial and repeatable success has been achieved to date only with patterns that, when set within a flask, permit dry unbonded sand to be easily introduced therein or therearound and which will occupy all voids within and without the patterns. However, if the part to be cast requires internal cored parts, the concept of cavityless casting is hampered.
Typically a core for other methods of conventional casting requires a core box into which resin mixed sand is introduced or blown and compacted to form a self-sustaining sand core having green strength sufficient to be transported from the core box to the molding flask for suspension therein. In the case of the cavityless method of molding, such resin bonded sand cores have been prepared in the past by the separate core box method and introduced to the interior of a consumable type pattern which has been split or bifurcated for introduction of the core therein. However, this detracts from one of the principal advantages of the cavityless method which is its use of dry, unbonded sand and the ease with which such sand falls away from the metal casting when metal solidification is complete contributing significantly to reduced finishing costs for the cavityless method. The cost of using separate core boxes, which must be cleared of sand after the core making operation, is undesirable. The requirement for curing of the sand cores with a binder mixed within the sand leading to the non-reuseability of the sand for purposes of the general cavityless method is also undesirable. Furthermore, the green strength of such cured sand cored parts leave much to be desired as to handling strength.